Solid-phase immunodetermination is usually performed in one vessel so that the analyte to be determined and possibly contained in the sample is first allowed to react with a separating reagent bound in a solid phase, whereupon the other steps required in the determination are performed in the same vessel. The troublesome thing here is that much dosing and removing of liquids must be performed. When several different determinations are done, a large stock of different reagents is also needed.
A system is also known wherein the solution to be used in each determination step is placed in advance in its own vessel. The solid phase is formed by the inside surface of a disposable pipette jet. In each step the pipette jet is brought into the respective vessel, the solution is drawn into the jet and a reaction is allowed to take place, whereafter the jet is emptied and moved into the next vessel. During the step of solution is moved back and forth in the jet. The equipment has several suction cylinders with pumps so that several determinations can be performed in parallel. No exact dosing devices are required in this equipment. Nor are any reagent containers required in the equipment. However, the drawback is that through a vapour phase samples are in connection with the cylinders of the equipment which can not, however, be washed automatically. This can cause a risk of contamination. Liquid will also remain in the pipette jet and will move along to the following step. In addition, piston pumps wear easily and unpredicatably, for which reason their condition must be checked often. Another problem is the sealing of the pipette jet to the suction cylinder. All things considered, much trouble can occur in this device. Besides, there is only limited solid-phase surface area available on the inner surface of the pipette jet.